Malignant tumors are often treated by surgical resection to remove as much of the tumor as possible. Infiltration of the tumor cells into normal tissue surrounding the tumor, however, can limit the therapeutic value of surgical resection because the infiltration can be difficult or impossible to treat surgically. Radiation therapy can be used to supplement surgical resection by targeting the residual tumor margin after resection, with the goal of reducing its size or stabilizing it. Radiation therapy can be administered through one of several methods, or a combination of methods, including external-beam radiation, stereotactic radiosurgery, and brachytherapy. The term “brachytherapy,” as used herein, refers to radiation therapy delivered by a source of therapeutic rays inserted into the body at or near a tumor or other proliferative tissue disease site.
A typical breast brachytherapy radiation treatment involves insertion of an applicator by a surgeon. A brachytherapy applicator may typically include a flexible catheter shaft with an inflatable balloon mounted on its distal end. One or more dosing lumens extend within the catheter shaft and into the balloon. The catheter shaft is inserted into a body so that the balloon is positioned within a resected cavity. The balloon is subsequently inflated and radioactive material, for example in the form of one or more radioactive seeds, is loaded into one or more of the dosing lumens for radiation delivery. The brachytherapy catheter system is removed upon completion of treatment. In single lumen brachytherapy treatment devices the dosing lumen is positioned along a central axis of the balloon such that substantially symmetrical isodose profiles may be achieved during treatment, i.e., a radiation dose of equal intensity is delivered to the tissue surrounding the balloon. In multi-lumen brachytherapy treatment devices one or more lumens are offset from the central axis within the balloon such that asymmetrical isodose profiles may be achieved during treatment, i.e., a radiation dose of greater intensity is delivered to certain areas of tissue surrounding the balloon in comparison to other areas, which receive a dose of lesser intensity. Proper orientation of the treatment device is desirable for delivering an asymmetric isodose profile. A physician may be able to make minor adjustments by applying direct rotational force to the shaft by hand. However, the catheter shaft may be ill-suited to transmitting torque. For example, a flexible shaft may initially twist in response to rotational force and then unpredictably untwist as applied resistance to twist increases and torque exceeds friction between the applicator and tissue. As a result, it is difficult to precisely orient the applicator.